JPH0311984Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a hands-free telephone device, and particularly relates to a control circuit for a hands-free telephone device installed in a telephone set housed in a telephone exchange device such as a button telephone device. be.

(Prior art and problems) The so-called voice switching type hands-free communication device has a transmitting/receiving level comparator that compares the levels of the transmitting voice and the receiving voice, and a transmitting/receiving level comparator that selectively attenuates the transmitting voice and the receiving voice. It has an attenuator to
The output of the reception level comparator controls the attenuator to increase the amount of attenuation of the lower level sound, thereby giving priority to the transmission of the higher level sound, thereby improving the acoustic coupling between the microphone and the speaker. This prevents the ringing (so-called howling) that would otherwise occur and allows two-way loudspeaker communication.

When a telephone equipped with such a hands-free calling device is housed in a telephone exchange to make a hands-free call, the call is a call between telephones housed in the telephone exchange (extension call); Due to the difference in the line length of the communication path, the following cases occur when a call is made between a telephone housed in the above-mentioned telephone exchange equipment and a telephone set via an external telephone line such as a central office line (outside line call). This will cause inconvenience.

In other words, when there is no sound (when the transmitting and receiving sounds are interrupted), the two input terminals of the transmitting and receiving level comparator (the transmitting level input terminal and the receiving level input terminal)
are at the same potential, so when a transmitting level input or a receiving level input is received, the potentials of both terminals rise from the same level. For internal hands-free calls, the line length is short, so when sending and receiving calls occur at the same time, the receiving level is often higher than the sending level (this tendency is especially true when the other party is using a handset). (This is remarkable in the case of a telephone call).As mentioned above, as the transmitting level input terminal and the receiving level input terminal rise from the same potential, the receiving side, which has a high proportion of inputs at a high level, becomes dominant. Therefore,
For example, the receiving state may continue due to background noise on the other party's side, making it difficult for the hands-free caller to enter the transmitting state. (If you don't increase the level) it will be difficult to make calls. For this reason,
For example, if the transmitting audio level is increased using an amplifier, etc., the receiving audio level will be relatively low in an outside line call with a long line length, so contrary to the above, the transmitting side will have an advantage and the hands-free calling side will This makes it difficult to receive the call.

In this way, conventional hands-free control circuits
If it were possible to make hands-free calls on both external lines and internal lines with different line lengths, there would be a problem in that the convenience would be halved.

(Purpose of the invention) The present invention is proposed to solve the above-mentioned problems, and provides a hands-free control circuit that allows good hands-free calls for both internal and external calls, which have different line lengths. The purpose is to

(Disclosure of the invention) For the above purpose, the invention provides a level raising means for making the transmitting level input of the transmitting/receiving level comparator higher than the level output from the previous stage,
This level raising means is controlled to connect/disconnect from the transmitting/receiving level input terminal of the transmitting/receiving level comparator by a switch means which is turned on/off according to outside call information or internal call information.

(Configuration of Example) FIG. 1 is a circuit diagram showing an embodiment of the present invention.

As shown in FIG. 1, the hands-free control circuit according to the embodiment compares the levels of the receiving level signal input to terminal 1 and the transmitting level signal inputted to terminal 2, and transmits and receives the voice to terminal 3. A transmitting/receiving level comparator (hereinafter referred to as a comparator) 4 that outputs a switching control signal, and a receiving level input terminal A of this comparator 4
A capacitor 5 and a resistor 6 are connected to the transmitting level input terminal B of the comparator 4 to smooth the receiving level signal, a capacitor 7 and a resistor 8 are connected to the transmitting level input terminal B of the comparator 4, and the resistor 8 is connected to the transmitting level input terminal B to smooth the transmitting level signal. Level raising means (a diode is used in the embodiment) is connected in series and acts to increase the transmitting level by adding a set DC level to the transmitting level signal input to terminal 2. Hereinafter, a diode will be taken as an example.) 9 and a resistor 10,
It is turned on or off by the control signal (internal/external line identification signal) input to the terminal 11, and the diode 9
and a resistor 10 (a transistor is used in the embodiment. Hereinafter, a transistor will be taken as an example) 1
2. It is composed of an input resistor 13 of this transistor 12, etc.

(Operation of the Embodiment) During an extension call, a low-level signal is input to the terminal 11 from the telephone exchange or the control device of the telephone to identify that the call is an extension call. As a result, the transistor 12 is turned off, and the series circuit of the resistor 8, diode 9, and resistor 10 is connected to the transmit level input terminal B of the comparator 4. When a transmit level signal is input to terminal 2 in this state, the level applied to input terminal B of comparator 4 is determined by adding the forward voltage of diode 9 to the level of the signal output from the previous stage of terminal 2. level. That is, in the operation of the comparator 4, the transmitting level signal shifts in a direction in which it becomes dominant by the level increase due to the forward voltage of the diode 9, and the receiving level signal becomes superior due to the short line length. As a result, it is no longer difficult to receive a call on the hands-free calling side.

Further, when an outside line is being used, a high level signal is input to the terminal 11 from the telephone exchange device or the telephone control device to identify an outside line call, which turns on the transistor 12. . Therefore, the series circuit of the diode 9 and the resistor 10 is equivalent to being short-circuited and disconnected from the input terminal B of the comparator 4. Therefore, unlike the above-mentioned extension call, the forward voltage level of the diode 9 is not added to the sending level signal, and it is no longer difficult for the hands-free caller to receive the call. During an outside line call, when the transistor 12 is turned on, a forward voltage is generated between its collector and emitter, but this forward voltage is considerably lower than the forward voltage of the diode 9, so it is difficult to use the hands while making an outside line call. This does not cause any problem in free control operation.

(Effects of the invention) As is clear from the above explanation, the present invention is effective in controlling the transmission level input to the comparator during hands-free internal or external calls using a telephone housed in a telephone exchange. The level increasing means is controlled to be connected to and separated from the transmitting level input terminal of the comparator so that either the receiving level input or the receiving level input is not biased to the dominant level. This is extremely effective in obtaining hands-free calls.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention. Main symbols: 4... Comparator, 9... Level increasing means (diode), 12... Switching means (transistor).

Claims (1)

[Scope of utility model registration request] installed in a telephone set housed in a telephone exchange equipment,
Transmitting and comparing the transmitting and receiving audio levels
In a voice switching type hands-free communication device having a receiving level comparator and switching between transmitting and receiving based on the output of the transmitting/receiving level comparator, it is possible to distinguish between an external call and an internal call. A switch means that is turned on and off by a signal is connected to the transmit level input terminal of the transmit/receive level comparator by the operation of the switch means during an internal call, and the signal input to the transmit level input terminal is connected to the transmit level input terminal of the transmit/receive level comparator. A hands-free control circuit having a level raising means for raising the level higher than the level output from the previous stage.